It is known that electrical conductors must be attached at appropriate contact points on substrates, such as circuit boards, micro-controllers and microprocessors, in order to establish electrical connections to some other contact point.
An electrical conductor is often attached by so-called bonding, which is understood to mean that a continuous material connection between the contact point and the electrical conductor is produced by ultrasonic friction welding. Using selected guidance, a tool head then guides the electrical conductor along a specified path curve to the second contact point, where it is attached in the same manner and then cut off from the supply of the electrical conductor, thereby producing an electrical connection of two contact points of a subassembly, such as a printed board assembly of a control device.
Two basic types of bonding connections are known. In so-called ball bonding, prior to attaching the electrical conductor, material from the electrical conductor is fused onto the first of the two contact points through heat input to the tip of a bonding tool, thereby producing a ball of material that is cohesive with the remaining electrical conductor. This ball may then be joined to the first contact point by bonding or ultrasonic friction welding. In contrast, no ball of material is produced in so-called wedge bonding. The electrical conductor is placed directly on top of the contact point, pressed onto it with a defined contact force, whereupon the ultrasonic energy is introduced to implement the friction welding.
To connect two contact points to an electrical conductor that is supplied continuously, at least one connection is expediently implemented as wedge bond, so that wedge-wedge bonds and ball-wedge bonds are basically conceivable.
In particular in ball-wedge bonding, the ultrasonic energy is introduced via linear vibrations, parallel to the substrate plane. The wedge side of the bond is then more difficult to produce than the ball side. The quality of the bond depends on the material and the surface of the contact point, the topography and the direction from which the ultrasonic energy is introduced. Following the ball-bonding at the first contact point, the tool head may be displaced in any direction relative to the substrate surface. A direction change of the tool, in particular of the bond head, is not required. A specific alignment with respect to the vibration direction of the linear ultrasonic vibrations and the respective travel direction, in particular the final travel direction, and the orientation of the electrical conductor prior to reaching the second contact point is not specified.
When introducing the ultrasonic energy in the production of a wedge bond, it should be noted that the vibration direction of the bonding tool relative to the extension of the electrical conductor has a different effect on the bond quality in the region of the contact point. Depending on the direction from which energy is introduced (angle between wire and vibration direction), correction factors for the possibly occurring power loss must be taken into account. The alignment of the bonding tool with respect to the extension of the conductor in the region of the contact point requires additional displacement movements of the tool head, thus causing a longer displacement time of the tool head. This increases both the manufacturing time and the production cost. On the other hand, estimating and taking the power loss into account is not sufficiently reliable to produce bonds that are strong and durable under all circumstances.
Therefore, it is an object of the present invention to provide a device and a method for producing high-quality bonding connections. In particular, it is an objective to realize the lowest possible machining period in so-called ball-wedge bonding.